Two-dimensional subpicosecond time-resolved fluorescence anisotropy: Optical Kerr-gating with the excitation of alternating polarizations of light

We have developed a subpicosecond time-resolved fluorescence anisotropy (TRFA) that newly implements a photoelastic modulator to alternate the polarizations of an excitation laser light. The setup facilitates virtually simultaneous detection of the parallel I∥I∥ and the perpendicular I⊥I⊥ emission from a photoexcited molecule of interest by means of an ultra-short (optical Kerr-gating) shutter and a spectrograph coupled with a charge-coupled device. From a set of I∥(λ,t)I∥(λ,t) and I⊥(λ,t)I⊥(λ,t) that comprise 2-D (two-dimensional) information on both a full range of spectra and subpicosecond time-resolved fluorescence decays, the 2-D TRFA, R(λ,t)R(λ,t), is directly given with better accuracy. To claim the merit of the technique we carried out a test for 2-D TRFA of Coumarin 153 in methanol.